1. Field of the Invention
The present invention relates to an expandable metal-pipe bonded body and a manufacturing method thereof, and more particularly, to an expandable metal-pipe bonded body well adaptable for plant pipes and line pipes, which are used in chemical industry and petrochemical industry, and oil-well tubes, such as casing tubes, production tubes, and coiled tubes, which are used in the oil well, and a method of manufacturing such an expandable metal-pipe bonded body.
2. Description of the Related Art
Long metal pipes have been used for a long distance transportation of corrosive fluid in the fields of chemical and petrochemical industries. The pipe line is used for transporting crude oil from an oil field to a refinery, and its length ranges into several tens Km.
To drill an oil well, a steel pipe, called a casing, is inserted into a bore hole in order to protect the bore hole drilled in the ground and to prevent crude oil from leaking. The oil well is located usually several thousands meter under the ground. Therefore, it is required to use a casing of several thousands meter long.
A seamless steel pipe of good corrosion proof is generally used for the metal pipe exposed to a corrosive atmosphere. The seamless steel pipe mass-produced is 10 to 15 m long, and the longest seamless steel pipe that can be manufactured is approximately 100 m at most. For this reason, a pipe bonded body as a string of seamless steel pipes of 10 to 15 m long is used for the line pipe or the oil-well tube, such as a casing.
A screw connecting method (mechanical bonding method), a welding method (orbital welding method), and a diffusion bonding method are typically known for the bonding method of bonding those metal pipes applied to such a use.
It is a common practice that a pipe bonded body formed by bonding a plurality of metal pipes of a given length in series (referred to as a metal-pipe bonded body) is used as intact or without increasing or decreasing the inside diameter of the bonded body. A metal-pipe bonded body having a desired inside diameter is generally formed by bonding metal pipes of the desired inside diameter in a string.
The casing for the oil well is buried in the ground, while the line pipe is laid on the ground. Accordingly, if the metal-pipe bonded body of a given inside diameter, while not altered, is used for the casing, the following problem arises.
It is technically difficult to dig into the earth toward an oil well laid several thousands under the ground in a state that the bore hole dug remains naked. For this reason, the oil well drilling work is done while repeating the following three steps: a first step of drilling a bore hole in the ground by use of drill pipe with a bit attached atop it, a second step of inserting a casing into the bore hole to protect the dug bore when the bore reaches a certain depth, and a third step to fix the casing by pouring cement into the gap between the inserted casing and the stratum. As a result, a plurality of casings are telescopically bonded in the oil bore.
A typical structure of the oil well is illustrated in FIG. 6. An oil well 10 exemplarily shown in FIG. 6 is constructed with four casings; a conductor pipe 12, a surface casing 14, an intermediate casing 16, and a production casing 18. The conductor pipe 12 has the largest outside diameter and functions to protect the bore wall located in the vicinity of the land surface. The surface casing 14 is telescopically inserted into the conductor pipe 12. The production casing 18, which is the longest of those casings, ranges to an oil stratum.
When the second casing (referred to as an xe2x80x9cinside casingxe2x80x9d) is inserted into the oil bore through the first inserted casing (referred to as an xe2x80x9coutside casingxe2x80x9d) (the first casing=first inserted casing, the second casing=subsequently inserted casing), the inserting of the second casing into the first casing is difficult when those casings are not aligned with each other axially or either of those casings is irregular in shape. To avoid this disadvantage, it is necessary to select the outside diameter of the inside casing to be smaller than the inside diameter of the outside casing by 10 to 30%.
A production efficiency of the oil well depends on the inside diameter of the production casing ranging to the oil stratum. To secure a given production efficiency, it is necessary not only to set the inside diameter of the production casing at a predetermined value, but also to set the inside diameter of the previously inserted casing at a large value. For this reason, the inside diameter of the oil bore dug near the land surface needs to be large, resulting in increase of oil-well drilling cost.
A solution to the problem is disclosed in TOKU HYOU HEI. 7-507610. In the solution, a casing made of malleable material is inserted into a bore hole dug in the earth, and the casing is radially expanded and pressed against the bore hole wall by expanding a hydraulic expansion tool placed within the casing.
Another solution is disclosed in WO 98/0062. In the solution, a steel pipe, which is made of malleable steel of the type which exhibits strain hardening without yielding necking and ductile fracture, is inserted into a bore hole or a casing previously inserted, and the casing is radially expanded by use of a mandrel with a tapered face, made of nonmetallic material.
Those solutions of TOKU HYOU HEI. 7-507610 and WO98/0062 allow the insertion of the inside casing of which the outside diameter is smaller than the inside diameter of the bore hole or the outside casing. Therefore, a smooth insertion work of the inside casing is secured.
In those techniques, the inside casing, which is inserted into the bore hole or the outside casing, is radially expanded by use of a hydraulic expansion tool or a mandrel. Therefore, almost the entire cross sectional area of the bore hole may be utilized for transporting crude oil. Further, the effective cross sectional area of the bore hole is increased in those techniques. With this feature, the inside diameter of the bore hole to be dug may be reduced, leading to reduction of digging cost.
Furthermore, as disclosed in TOKU HYO HEI. 7-507610, when the casing is radially expanded and pressed against the bore hole wall, the casing is firmly held by compression stress induced by the bore hole wall. Therefore, there is no need of cement work.
As described above, the casing used for the oil well is considerably long, reaching to several thousands meter, and indispensably includes the bonding portions, However, those are no taken into consideration in TOKU HYO HEI. 7-507610 and WO 90/0062.
When the metal pipes are bonded into a metal-pipe bonded body by the welding bonding method or the metallurgical bonding method, such as the diffusion bonding method, the heating during the bonding process causes a heat affected portion to occur. In this state, a deformability of the bonding portion possibly reduces, and therefore the bonding portions may be cracked when the resultant metal-pipe bonded body is radially expanded by use of a mandrel.
When the metal pipes are bonded into a metal-pipe bonded body by the screw connecting method, and the resultant metal-pipe bonded body is radially expanded by a mandrel, a plastic deformation caused at the time of the expanding of the bonded body loosens the screw-bonded portion, resulting in the air-tightness at the bonding portion.
Illustration useful in explaining the screw connecting method is given in FIG. 7. As shown, outside threads 1a and 2b are formed the outer surfaces of the end portions of metal pipes 1 and 2. Those metal pipes are bonded together by means of a joint 7 having an inside thread 7a. The bonding portion of the metal-pipe bonded body is thicker than the non-bonding portion. When the metal-pipe bonded body thus configured is radially expanded by use of a mandrel, a deformation resistance at the bonding portion is increased, impeding the pipe expanding work.
When a metal-pipe bonded body of several thousands meter long, which is uniform in inside diameter over its entire length, is radially expanded at a dash, a reaction force constantly acts in the mandrel during the course of its moving within the bonded body. Under this condition, a large force is required for moving the mandrel.
A technique to solve the problem is disclosed in WO98/0062. In the technique, the tapered surface of the mandrel is made of nonmetallic material, such as ziruconia. With this, a frictional force between the mandrel and the casing is reduced. If the technique is used, the reaction force constantly acts in the mandrel during the course of its moving, and hence the technique still presents an unsatisfactory solution to the power saving problem.
The technique of TOKU HYO HEI. 7-507610 repeats a sequence of the following steps: a hydraulic expansion tool is set at a given position within the casing; it is operated to expand only the casing located at that position; it is stopped in its expanding operation; it is moved downstream within the casing; and it is operated again. This technique solves the power saving problem when comparing with the case where the casing is radially expanded at a dash by use of the mandrel. Thus, the technique stepwise expands the casing, and hence the working efficiency is poor.
When the metal pipes are bonded into a metal-pipe bonded body by the diffusion bonding method, it is a common practice that only the end faces of the metal pipes are machined to be flat, and those metal pipes are bonded together without altering the outer circumferential surfaces and the thickness of the metal pipes. The metal pipes industrially manufactured are indispensably attendant with given dimensional tolerances. In other words, the outside diameter and the thickness of the metal pipes are varied in value-within the tolerances.
When the metal pipes mass-produced are bonded as intact by the diffusion bonding method, steps or stepped portions will be formed on the bonding portions of the resultant metal-pipe bonded body. Stress tends to concentrate at the steps. Therefore, such a bonded body is radially expanded, the bonding portions will be cracked from the steps. If the steps are left there after the pipe expansion. Concentration of stress at the steps continues and corrosive material is likely to stay there. The result is to lessen a strength of the bonded body, and to deteriorate the fatigue characteristic and the corrosion resistance of the bonded body. Any specific technical means to solve such problems is not found in the background art described above.
To achieve both the oil well drilling cost and the productivity, there is proposed a pipe expanding method in which a metal-pipe bonded body of which the outside diameter is smaller than the inside diameter of a bore hole dug in the ground is inserted into a bore hole, and it is radially expanded uniformly over its length by use of a mandrel (for example, WO No. 98/0062).
This pipe expanding method include the steps as shown in FIG. 13A. A metal-pipe bonded body 122 is inserted into a bore hole 124 dug in the ground. The inside diameter of the metal-pipe bonded body is uniform over its length and smaller than the inside diameter of the bore hole 124.
A tapered mandrel 126 is inserted into the metal-pipe bonded body 122 from the upper end 122a thereof (FIG. 138). A shaft 128 is bonded to the bottom surface of the mandrel 126 in the case of FIG. 13B. The shaft 128 is used for inserting the mandrel 126 into the metal-pipe bonded body 122. With the metal-pipe bonded body 122, the mandrel 126 is moved toward the other end of the metal-pipe bonded body by use of the shaft 128 (FIG. 13C. In this way, the metal-pipe bonded body 122 is increased in its inside diameter uniformly over its length.
In addition to the pipe expanding method in which the mandrel 126 is moved by use of the shaft 126 attached to the bottom surface thereof, another pipe expanding method is known. In this method, a mandrel not having the shaft is inserted into the metal-pipe bonded body 122, and is hydraulically moved therewithin (not shown).
The pipe expanding method of FIGS. 7A to 7C allows the insertion of an inside casing smaller in inside diameter than the inside diameter of the bore hole or the outside casing, and hence has an advantage of a smooth insertion of the inside casing.
The inside casing smaller in inside diameter than the inside diameter of the bore hole or the outside casing is radially expanded by use of the mandrel. Therefore, the method is advantageous in that the most part of the cross sectional area of the bore hole can be utilized for transporting crude oil. The advantage accrues to the reduction of the inside diameter of the bore hole actually dug and hence to bore-hole digging cost.
The pipe expanding method suffers from the following disadvantages. Insertion of the mandrel 126 into the metal-pipe bonded body 122 having a uniform inside diameter, from its upper end 122a is accompanied with large deformation resistance. Therefore, when the mandrel 126 is performed inserted into the metal-pipe bonded body 122 being buried in the ground, excessive force exerts on the metal-pipe bonded body 122, to deform or break the metal-pipe bonded body 122 per se. Great care is used for the insertion work of the mandrel 126, resulting in poor working efficiency.
In the pipe expanding method in which the mandrel is moved by hydraulic pressure, a tightly closed space must be formed in the upper end 122a of the metal-pipe bonded body 122. To this end, a flange, for example, must be welded to the upper end 122a of the metal-pipe bonded body 122.
The welding work for the flange fixing is dangerous in an environment where flammable gas is present since arc generated in the welding operation will ignite the flammable gas. Particularly the oil well field requires a minimum welding work on job site.
In the mechanical bonding method, metal pipes the threaded end portions are bonded end to end by a screw bonding manner. This bonding method takes 5 to 10 minutes for bonding one joint, and is advantageous in that the metal-pipe bonding work efficiency is high, but is disadvantageous in that leakage of oil or gas from the bonding portion is easy to occur. For this reason, the metal pipe needs to be machined with high precision and the bonding work needs high skill. Further, much care is used for transportation of the high precision metal pipes to avoid damage of the metal pipe. Furthermore, the screw-bonded portions are resistive to tensile stress. However, those portions are likely to radially expand when compression stress exerts thereon, to promote leakage of oil or gas therethrough.
In the orbital welding method, to bond the metal pipes, the end-faces of the metal pipes are beveled; and the metal pipes with the beveled ends are bonded together at their ends; and the bonded and beveled ends of those metal pipes are padded with molten metal. The metal-pipe bonded body produced by the welding method is free from oil or gas leakage unless the welding portions suffer from poor welding or pin holes, and further is resistive to tensile stress and compression stress. Disadvantages of the welding method follows. There is a limit in increasing the welding efficiency. Particularly in the case of welding thick metal pipes, the multi-layer welding is required, and takes 1 to 2 hours for welding one joint. Additionally, the welding work on the job site is influenced by weather, wind and other environmental conditions, and further requires highly skilled welding technique.
A frictional bonding method is also known. In this bonding method, butted metal pipes are rotated relative one to the other. Frictional heat generated during the metal-pipe rotation softens the ends of the metal pipes, and the softened ends are bonded together by press. Advantages of the frictional bonding method are that a less skill is required when comparing with other bonding methods; short time is taken for the bonding, and the bonding work is little affected by environmental conditions. A decisive disadvantage of this bonding method is that the inside and outside surfaces of the press-bonded portions is inevitably burred, and much time is taken for removing the burrs. An unsatisfactory solution to the burr problem was proposed. In the solution, a ring wedge-shaped in cross section is inserted between the end faces of paired metal pipes. The ring is pushed toward the center of the paired metal pipes (when viewed in cross section) while rotating the ring in a state that the paired metal pipes are fixed, whereby those metal pipes are press bonded together. The characteristics of the press-bonded joint are not satisfactory.
The diffusion bonding method follows. In this method, two metal pipes are butted; the abutting ends of the metal pipes are heated at a temperature below their melting point while being pressed together; in this state elements of the metal pipes are diffused at the bonding interface, whereby the metal pipes are bonded together. The diffusion bonding method is classified into a xe2x80x9csolid-phase diffusion bonding methodxe2x80x9d and a xe2x80x9cliquid-phase bonding methodxe2x80x9d. Either of those methods may be used for the diffusion bonding method. In the former bonding method, the ends of metal pipes are bonded together, and elements of the material of the metal pipe are diffused in a solid-phase state of the material. In the latter bonding method, an insert member is inserted between the bonding surfaces of the metal pipes, and the insert member is molten to diffuse elements from the molten insert member into the metal pipes.
The diffusion bonding method is advantageous in that no leakage of oil or gas from the bonding portions occurs if the bonding is performed under proper bonding conditions, and the bonding portions are resistive to compression stress as in the welding method, and further that the bonding time for one joint (bonding portion) is short, ⅓ to xc2xd as long as of the welding method. In this respect, the diffusion bonding method is excellent when it is applied to the bonding of oil well tubes and line pipes.
When the metal pipes are bonded into a metal-pipe bonded body by the diffusion bonding method, it is a common practice that only the end faces of the metal pipes are machined to be flat, and those metal pipes are bonded together without altering the outer circumferential surfaces and the thickness of the metal pipes.
The metal pipes industrially manufactured are indispensably attendant with given dimensional tolerances. In other words, the outside diameters and the thickness values of the metal pipes are varied in value within the tolerances. When the metal pipes mass-produced are bonded as intact by the diffusion bonding method, steps will be formed on the outer surfaces and/or the inner surfaces of the bonding portions of the resultant metal-pipe bonded body.
When the bonded body of which the bonding portions have steps is used as intact, stress tends to concentrate at the steps or stepped portions, the bonding portions will be cracked from those steps or the steps are likely to be start point of fatigue crack. Further, corrosive materials strays at the steps on the inner surfaces of the bonding portions, and will adversely affect the mechanical characteristic and corrosion resistance.
The steps formed on the outer surfaces of the bonding portions can be removed after the bonding process ends, but removal of the steps on the inner surfaces of the bonding portions is difficult.
It is an object of the present invention is to provide an expandable metal-pipe bonded body which is free from cracks of the bonding portions of the bonded body and reduction of the air-tightness of the bonding portions caused by loosening of the screw bonding, and a manufacturing method thereof, when the bonded body is radially expanded.
It is an object of the present invention to provide an expandable metal-pipe bonded body which is low in deformation resistance when the bonded body is radially expanded, and requires less power in the expanding process of the bonded body, and a manufacturing method thereof.
It is an object of the present invention is to provide an expandable metal-pipe bonded body which reduces the steps at the bonding portions thereof, and is excellent in strength, fatigue characteristic and corrosion resistance, and a manufacturing method thereof.
It is an object of the present invention to provide an expandable metal-pipe bonded body in which in radially expanding the bonded body, the pipe expanding tool is smoothly inserted into the bonded body without breaking and deforming the bonded body, and danger of igniting the flammable gas is minimized in the pipe expanding work at the oil well.
It is an object of the present invention to provide a method of bonding metal pipes bonded end to end by a diffusion bonding method which reduces steps at the bonding portions, and is excellent in strength, fatigue characteristic and corrosion resistance.
The present invention provides an expandable metal-pipe bonded body formed by bonding a plurality of metal pipes in a series, in which the inside diameter of each bonding portion of each of the metal pipe is larger than the inside diameter of the non-bonding portion of each of the metal pipe.
Such an expandable metal-pipe bonded body may readily be manufactured by increasing the inside diameter of the end portion of each of metal pipes, and bonding together the metal pipes in a string fashion. In this case, it is preferable that the inside diameter of each end portion of each of the metal pipe is increased so as to have an pipe-end expansion rate of 5% or greater. If the pipe-end expansion rate is less than 5%, there is a danger that the jointing or bonding portions will be cracked when the bonded body is radially expanded. The bonding method is preferably a diffusion bonding method or a welding method.
An expandable metal-pipe bonded body may be produced by increasing the inside diameter of the end portion of each of metal pipes, threading the end portion of each of the metal pipe, and mechanically bonding the metal pipes with the aid of the threaded end portions. In this case, it is preferable that the inside diameter of each end portion of each of the metal pipe is increased so as to have an pipe-end expansion rate of 10% or greater. If the pipe-end expansion rate is less than 10%, the screw bonding portions are plastically deformed when the bonded body is radially expanded, leading to impairing the air-tightness at the bonding portions.
An expandable metal-pipe bonded body may be manufactured by butting metal pipes, the end portions of the metal pipes being not increased in their inside diameter, and bonding together the butted end portions of the metal pipes by a diffusion bonding method under such a bonding condition that the end or bonding portions are laterally expanded. In this case, it is preferable that the bonding portions of the metal pipes are diffusion bonded so as to have a lateral expansion rate of 1.04 or greater. If the lateral expansion rate is less than 1.04, when the bonding or bonded body is radially expanded, the bonding portions will be cracked possibly.
In the thus constructed expandable metal-pipe bonded body, the inside diameter of each bonding portion of each of the metal pipe is larger than the inside diameter of the non-bonding portion of each of the metal pipe. When the metal-pipe bonded body is radially expanded by a mandrel, a plastic deformation of the bonding or joining portion is smaller than that of the non-bonding or non-joining portion.
When the metal pipes in which the inside diameter of each bonding portion of each of the metal pipe is larger than the inside diameter of the non-bonding portion of each of the metal pipe is butted and bonded or bonded by the diffusion bonding method or the welding method into a metal-pipe bonded body, and the resultant bonded body is radially expanded, thermally affected portions are created in the bonding portions and hence their deformability is reduced. However, the metal-pipe bonded body is substantially free from cracking of the bonding portions which will possibly occur when the bonded body is radially expanded.
When the metal pipes of which the end portions are not radially expanded are bonded end to end, and jointed by the diffusion bonding method while at the same time those jointing portions are radially expanded, at a predetermined lateral expansion rate, into a barrel shape by pressure applied in this process, to thereby form a metal-pipe bonded body, cracking in the bonding portions is hard to occur, and additionally there is eliminated a step of increasing the inside diameter of the metal pipe.
When metal pipes of which the end portions are increased in inside diameter at a predetermined pipe-end expansion rate are bonded, by the screw connecting method, into a metal-pipe bonded body, and the resultant bonded body is radially expanded at a pipe expansion rate smaller than the pipe-end expansion rate, there is no chance of plastic deformation of the screw bonded portions. Therefore, there is eliminated reduction of the air-tightness, which is caused by loosening of the screw portion.
In the metal-pipe bonded body of the invention, the inside diameter of the bonding or joining portion of the metal pipe is larger than that of the non-bonding or joining portion. Because of this, a deformation resistance in the joining portion is reduced. This ensures a smooth pipe expanding work and saves the required power.
When the end portions of the metal pipes are radially increased at a predetermined pipe-end expansion rate, those metal pipes are bonded end to end and jointed together into a metal-pipe bonded body, the radial expansion work may uniformize the inside diameter values of the metal pipes. Therefore, if the metal-pipe bonded body is produced by use of the metal pipes having variations of the outside diameter and the thickness of them, the steps formed in the bonding portions may be reduced. The resultant metal-pipe bonded body is excellent in strength, fatigue characteristic and corrosion resistance.
The present invention further provides an expandable metal-pipe bonded body formed by bonding a plurality of metal pipes in a series, in which the end of the metal-pipe bonded body is bonded to a metal pipe of which the non-bonding end is set in advance to be larger in inside-diameter than the central portion.
It is preferable that the inside diameter of the non-bonding end of each of the metal pipe to be bonded to the end of the metal-pipe bonded body is larger than the outside diameter of a pipe expanding tool for expanding the inside diameter of the metal-pipe bonded body uniformly over its length bonded body. In the specification, the term xe2x80x9cnon-bonding endxe2x80x9d of the metal pipe bonded to the end of the metal-pipe bonded body means the end portion of the metal pipe which is not bonded to the metal-pipe bonded body.
In the expandable metal-pipe bonded body, the end of the metal-pipe bonded body is bonded to a metal pipe of which the non-bonding end is set in advance to be larger in inside-diameter than the central portion. Therefore, smoother insertion of the tool is realized when comparing with the case where the inside diameter of the end portion of the metal-pipe bonded body is not increased.
Insertion resistance of the tool into the metal-pipe bonded body is reduced to zero when the inside diameter of the non-bonding end of each of the metal pipe to be bonded to the end of the metal-pipe bonded body is larger than the outside diameter of a pipe expanding tool for expanding the inside diameter of the metal-pipe bonded body. The result is that the smooth insertion of the tool is realized, and the bonded body is not broken and deformed.
Since a flange is applied in advance to the non-bonding end of the metal pipe to be bonded to the metal-pipe bonded body, there is eliminated the work of welding the flange to the metal-pipe bonded body. When the welding work is done for the flange fixing in an environment containing flammable gas, less danger of igniting the flammable gas is produced, securing a safety of the pipe expanding work.
The present invention provides a method of bonding metal pipes bonded end to end by a diffusion bonding method wherein the inner surface of the bonding end of at least one of metal pipes to be bonded together is machined so that an inside diameter difference between the bonding end faces of said metal pipes is smaller than 2 mm.
In the metal-pipe bonding method, the working of said inner surface is a diameter-increasing process not attendant with removal of material or a machining process attendant with removal of material. Alternately, it may be a combination of a diameter-increasing process not attendant with removal of material and a machining process attendant with removal of material.
In the metal-pipe bonding method of the invention, the inner surface of the bonding end of at least one of metal pipes to be bonded together is machined, before a diffusion bonding process commences, so that an inside diameter difference between the bonding end faces of said metal pipes is smaller than a predetermined value. Therefore, even if the outside. diameters and the thickness values of metal pipes vary in value before the bonding process starts and hence the inside diameter difference between those metal pipes is present, there is no chance that great steps are formed on the inner surfaces of the bonding portions. Accordingly, the resultant bonded body is improved in strength, fatigue characteristic and corrosion proof.